It is known that vortex valves can be used to regulate stormwater flow. For example, WO99/43899 discloses a vortex valve for regulating stormwater flow comprising a vortex chamber defined by a circular cylindrical wall and two axial end walls. The vortex chamber has an outlet through one end wall and an inlet arranged to cause swirl in the chamber when a certain critical flow has been attained.
At low flow rates, water entering through the inlet of a vortex valve passes through the vortex chamber to the outlet with substantially no pressure drop, and the valve can be considered to be open. At high flow rates, water enters through the inlet with enough energy to create a vortex in the vortex chamber which results in a significant pressure drop between the inlet and the outlet. The pressure drop generates an air-filled core at the center of the vortex which restricts flow through the outlet, and can even substantially cut it off altogether. The valve thus limits the rate of flow through the valve automatically. Vortex valves can be used, for example, to control the flow of stormwater in sewers so that equipment downstream of the valve is not overloaded during periods of heavy rainfall.
The performance of a vortex valve under particular flow conditions is dictated by the geometry of the vortex valve, for example the size of the inlet or outlet, or the diameter of the vortex chamber.
An important characteristic of a vortex valve is the relationship between the pressure head across the valve and the flow rate through the valve. The required characteristic is commonly specified by the customer. If a fixed geometry vortex valve is to be provided, the customer's requirement can sometimes call for the outlet of the vortex valve to have a relatively small diameter, which may be subject to blockage by debris entrained in the flow through the vortex valve. An increase in the diameter of the outlet to reduce the risk of blockage will increase the flow rate through the valve under storm conditions, and this may not be acceptable.
Also where a vortex valve is installed with standard pipe fittings, or retrofitted into an existing drainage system, the inlet/outlet of the valve must be sized to accommodate the diameter of the pipes to which the valve is connected. Consequently, in order to deliver the required performance, the geometry of the vortex chamber other than the inlet/outlet diameter, for example the diameter of the vortex chamber, must be designed to meet performance requirements. Vortex valves are thus often designed on an ad hoc basis for specific applications.
Furthermore, where the geometry of the valve is constrained by the inlet and outlet diameter requirements, the space in which the valve is fitted often has to be adapted to accommodate the valve. This is both costly and time consuming.